In the field of silver halide photographic materials, particularly for photography, high sensitive silver halide photographic materials having excellent picture quality have always been desired.
Various approaches for improving sharpness, which is the most important picture quality, have been known. One approach is to inhibit light scattering. Another is to improve the edge effect.
It is known that silver halide photographic materials having a dye in their constituent layers absorb light of a specified wavelength and inhibit light scattering. Because of this, it has been a conventional practice to color a hydrophilic colloidal layer with a dye.
More specifically, colloidal silver has been previously used to absorb yellow light and inhibit halation. However, colloidal silver does not provide a maximum increase in sharpness because incorporating it causes an increase in fogging of a light-sensitive silver halide emulsion layer adjacent to the colloidal silver layer.
In an approach described in International Patent WO 88/04794, a dye dispersion is used as a substitute for colloidal silver. Although this enables a reduction in the rise of fogging of the adjacent layers, it also causes a drop in the light-sensitive silver halide emulsion layer activity of solution physical development, which results in a drop in the edge effect, thus making it impossible to thoroughly improve sharpness.
It is known that sharpness can be improved by using silver halide emulsion grains having a diameter large enough for light scattering. However, grains with such a large diameter cause a deterioration in visual graininess.
Another known approach is to drastically reduce the coated amount of silver. However, in drastically reducing the coated amount of silver, the number of active points is reduced which causes a deterioration in graininess.
Other approaches similar to reducing the coated silver involve reducing the content of gelatin, couplers, or coupler solvents or the like in the coating solution. However, these approaches generally cause a deterioration in coating properties or color density.
Examples of approaches for improving the edge effect include the use of an unsharp mask and the use of DIR couplers for color negative films. The use of an unsharp mask is limited in its practicality because it is a complicated process. DIR couplers are known in many ways.
Examples of useful DIR couplers include the compounds described in JP-B-55-34933 (the term "JP-B" as used herein refers to an "examined Japanese patent publication"), JP-A-57-93344 (the term "JP-A" as used herein refers to a "published unexamined Japanese patent application"), and U.S. Pat. Nos. 3,227,554, 3,615,506, 3,617,291 and 3,701,793. However, if a DIR coupler is used to intensify the edge effect, Modulation Transfer Function (MTF) can be improved in a low frequency range, but MTF cannot be improved at the higher frequency ranges required for high power magnification. Furthermore, DIR couplers cause an undesirable side effect such as a sensitivity or density drop.
If a DIR coupler capable of attaining its effects at a remote distance, such as a diffusive DIR, is used, this drop of sensitivity or density can be reduced. However, this approach only causes a further shift in the MTF improvement range to the low frequency side. Thus, high power magnification cannot be expected.
As a result of extensive studies, the inventors found that the edge effect can be dramatically enhanced by increasing the silver density of the light-sensitive silver halide emulsion layer. However, this increases fogging as well as causes a deterioration in the preservability of the light-sensitive material.
In the present invention, the silver density of the light-sensitive silver halide emulsion layer is predetermined to a high range not only to enhance the activity of solution physical development which results in an increase in the edge effect and also to reduce the film thickness per unit of silver, providing an unexpected increase in sharpness. That is, sharpness is increased beyond the expected increase attained using each of the above approaches. The present process does not suffer from any deterioration in preservability, which has been heretofore unavoidable when the silver density is raised.